Question

Draw structural formulas for the cis and trans isomers of hydrindane. Show each ring in its most stable conformation. Which of these isomers is more stable?

Short answer

Answer: The trans isomer of hydrindane is more stable due to less steric strain as the bulky substituents are on the opposite sides of the ring junction, allowing for more space between them.

Step-by-step solution

Draw the basic structure of hydrindane

First, draw the basic structure of hydrindane, which is a cyclohexane ring fused to a cyclopentane ring.

Draw cis and trans isomers

For the cis isomer, the two hydrogens at the ring junction will be on the same side of the ring. For the trans isomer, the two hydrogens will be on opposite sides of the ring. Draw the cis and trans isomers of hydrindane, each showing hydrogen atoms across the ring junction. Cis isomer: H :_ - _: / \ :------------: Trans isomer: H :_ - _: \ / :------------:

Identify the most stable conformation for each isomer

Cyclohexane is most stable in its chair conformation, while cyclopentane is most stable in its envelope conformation. Represent each isomer in their respective most stable conformation. Cis isomer (chair and envelope conformation): H :_ - _: / \ :------------: Trans isomer (chair and envelope conformation): H :____::_/__\^ /:-----------:

Determine the more stable isomer

The more stable isomer is the one with the least amount of steric strain. The cis isomer has hydrogens on the same side of the ring junction, which results in more steric strain due to the bulky substituents in proximity. In contrast, the trans isomer has hydrogens on opposite sides of the ring junction, allowing for more space between the bulky substituents, resulting in less steric strain. Therefore, the trans isomer is more stable.